Creative thinking... (Spoiler)
It never occurred to me to use the chair. I used the rocket.
If I remember rightly I carried a cube from the last puzzle or somethig...
If not then the way valve meant, but I don't remember taking it from the tube...
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I was stuck on that level and eventually noclipped it. My friend told me to do the chair thing, but I would've never thought of blowing up the tube
me neither, I ran around that place for a while, trying to get up there.
Then I thought, hey there are stuff back there.
So I placed a portal near the vent (closest where I could) And walked back to the office and placed on there, 2 chairs trough the portal, putting the portals aside and stacking all the way 
The chair was the first thing that made sense. If it were real life I'd grab a chair...not blow up a tube of super-thick glass. Maybe if the glass had cracks all over it and looked breakable...or had wires dangling off of it to get my attention. I don't even think I noticed a tube there. :O
It was set shortly after you'd travelled through a broken cube tube and just after you learned that rockets can break glass.
Nyoobs
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